Detector array based optical systems for industrial inspection and machine guidance (machine vision) have been utilized. However, some problems do exist. A major problem is often related to light power. This is caused by a number of problems such as degradation of the lamps and accumulation of dirt or debris on windows, optics, parts, and others. Problems of this sort can be solved by building observed light power detectors into the system to compensate lamp power, array intergration time, or scan rate as a function of detected power through the window by the sensor unit.
However, many times the source of error also couples with a change in the object being viewed. For example, where a part is being veiwed by the machine, the part color can change due to a different casting supplier, parts running oily, or a faulty parts washer which leaves dirt or a wash residue on the part. In such situations, it is not sufficient to make a simple light level change since it is not known what the correct reflecting light level from the part should be. For example, if an operator uses a clean and dry master which is shiny to set the control system for the optical sensor, and the parts are dull, dirty or wet, incorrect settings of the optical system result.
In large range dimensional optical sensors, the sensor output is often nonlinear. It is therefore necessary to calibrate this output to determine the correct dimension. This is often difficult to do.